title: Monte Carlo-based parametrization of the lateral dose spread for clinical treatment planning of scanned proton and carbon ion beams.
abstract: Ion beam therapy using state-of-the-art pencil-beam scanning offers unprecedented tumour-dose conformality with superior sparing of healthy tissue and critical organs compared to conventional radiation modalities for external treatment of deep-seated tumours. For inverse plan optimization, the commonly employed analytical treatment-planning systems (TPSs) have to meet reasonable compromises in the accuracy of the pencil-beam modelling to ensure good performances in clinically tolerable execution times. In particular, the complex lateral spreading of ion beams in air and in the traversed tissue is typically approximated with ideal Gaussian-shaped distributions, enabling straightforward superimposition of several scattering contributions. This work presents the double Gaussian parametrization of scanned proton and carbon ion beams in water that has been introduced in an upgraded version of the worldwide first commercial ion TPS for clinical use at the Heidelberg Ion Beam Therapy Center (HIT). First, the Monte Carlo results obtained from a detailed implementation of the HIT beamline have been validated against available experimental data. Then, for generating the TPS lateral parametrization, radial beam broadening has been calculated in a water target placed at a representative position after scattering in the beamline elements and air for 20 initial beam energies for each ion species. The simulated profiles were finally fitted with an idealized double Gaussian distribution that did not perfectly describe the nature of the data, thus requiring a careful choice of the fitting conditions. The obtained parametrization is in clinical use not only at the HIT center, but also at the Centro Nazionale di Adroterapia Oncologica.
authors.affiliation: Heidelberg Ion Beam Therapy Center and Department of Radiation Oncology, Heidelberg University Clinic, Im Neuenheimer Feld 450, 69120 Heidelberg, Germany. Katia.Parodi@physik.uni-muenchen.de
authors.forename: Katia
authors.initials: K
authors.lastname: Parodi
authors.forename: Andrea
authors.initials: A
authors.lastname: Mairani
authors.forename: Florian
authors.initials: F
authors.lastname: Sommerer
mesh_terms: D000465:Algorithms; D002244:Carbon / Q000627:therapeutic use; D063193:Heavy Ion Radiotherapy / Q000379:methods*; D006801:Humans; D007477:Ions; D009010:Monte Carlo Method; D009369:Neoplasms / Q000532:radiotherapy; D016011:Normal Distribution; D061766:Proton Therapy / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D012984:Software
chemical_list: D007477:Ions; D002244:Carbon
keywords: Monte Carlo; ion therapy; lateral dose distribution; treatment planning